Dual-protein visual detection using ratiometric fluorescent probe based on Rox-DNA functionalized CdZnTeS QDs

Herein, we developed a simple and sensitive method for the detection of protamine and trypsin by using a ratiometric fluorescent probe based on Rox-DNA functionalized CdZnTeS quantum dots (QDs). The Rox-DNA functionalized CdZnTeS QDs were prepared via one-pot method, which was simple, low-cost, and modification-free. Protamine can cause the aggregation of ratiometric fluorescent probe through electrostatic interaction and quench the fluorescence of CdZnTeS QDs. Then, the protamine could be hydrolyzed to small peptides by trypsin and the fluorescence of QDs was recovered. However, the fluorescence of Rox kept unchanged. The fluorescence intensity ratio was proportional to the concentration of protamine or trypsin. A good linear relationship (25–300 ng/mL for protamine and 2.5–50 ng/mL for trypsin) with low limit of detection (4.73 ng/mL for protamine and 0.87 ng/mL for trypsin) was obtained. Meanwhile, we observed different colors by the naked eye after the addition of different concentrations of protamine and trypsin, and the minimum detectable concentration was as low as 4 μg/mL for protamine and 40 ng/mL for trypsin, respectively. In addition, the ratiometric fluorescent probe exhibited good analytical performance in complex biological matrix. Therefore, the ratiometric fluorescent probe can be proposed as a simple and effective tool for the detection and visualization of dual proteins.